The present invention relates to thrust vectoring techniques, and more particularly, but not exclusively, relates to techniques to control thrust vectoring and nozzle throat area with variable pitch guide vanes.
Typically, a jet powered aircraft is controllably propelled by thrust substantially parallel with and in a direction opposite working fluid exiting a nozzle. Consequently, if the direction of the working fluid is changed, the direction of propulsive thrust and the aircraft direction is corresponding varied. As used herein, "nozzle" means an aircraft passage or outlet for discharging working fluid to produce thrust.
With the advent of vertical or short take off and vertical landing (V/STOVL) aircraft, the need for efficient, uninterrupted vectoring of thrust has arisen. The hot gases exhausted from a gas turbine engine are one source of working fluid which may be vectored. Alternatively, "cold flow" from a lift fan may also serve as a working fluid source. Such a lift fan is typically driven indirectly by a coupling to a gas turbine engine. U.S. Pat. No. 5,209,428 to Bevilaqua et al. is cited as a source of further information concerning lift fan aircraft.
For the V/STOVL mode of aircraft operation, a continuous, uninterrupted vectoring of thrust is required throughout a wide angular range to provide lift for the aircraft. Also, a smooth and reliable transition to a horizontal cruise mode is often required. Moreover, as with most aircraft equipment, thrust vectoring systems generally must be lightweight, reliable, and compact, occupying as little space as possible. U.S. Pat. Nos. 5,769,317 to Sokhey et al.; U.S. Pat. No. 5,485,958 to Nightingale; U.S. Pat. No. 3,640,469 to Hayes et al.; U.S. Pat. No. 3,397,852 to Katzen; U.S. Pat. No. 3,179,353 to Peterson; and U.S. Pat. No. 2,989,269 to Le Bel illustrate various guide vane bank arrangements for vectoring thrust.
One typical drawback of these systems is the inability to selectively adjust the exit area presented to working fluid as it passes through the vanes while simultaneously and independently deflecting the exiting working fluid to vector thrust. The ability to select the working fluid exit area or throat area generally improves vectoring system efficiency.
One approach to this problem is to simultaneously adjust vectoring and throat area by using an independently controllable actuator for each vane in the bank. Unfortunately, this approach is often impractical because of the attendant increase in weight, complexity, and space required for the separate actuators.
Furthermore, proposed systems do not appear to account for changes in thrust efficiency of a given vectoring nozzle design that occur in response to changes in pivotal orientation of the vanes.
Thus, there remains a need for improved techniques to selectively vector thrust with a number of guide vanes.